The present invention relates to a ceiling built-in type air conditioner having a heat exchanger installed within a main body cabinet including an air suction inlet and an air blowing outlet.
FIG. 13 is a perspective view for showing a conventional ceiling built-in type air conditioner, and FIG. 14 is a transverse cross-sectional view thereof. In these drawings, 1 denotes a main body cabinet for forming an outer fence of the air conditioner, and this has an air suction inlet 2 and an air blowing outlet 3. 4 denotes a fin tube heat exchanger incorporated in the main body cabinet 1, and fins 5 of the heat exchanger 4 are vertically arranged in parallel with the flow of air within the main body cabinet 1. 6 denotes a casing provided outside the air suction inlet 2 of the main body cabinet 1, and an air blowing outlet of the casing 6 has a smaller area than that of an air suction surface in the front of the heat exchanger 4. 7 denotes a centriffigal blower provided inside the casing 6 and the length (width) of the centrifugal blower 7 in the axial direction is smaller than the length (width) of the heat exchanger 4. Further, 8 denotes a blower motor for driving the centrifugal blower 7.
Next, the flow of air of the prior-art ceiling built-in type air conditioner will be explained with reference to FIG. 15, FIG. 16 and FIG. 17. As shown in FIG. 15 and FIG. 16, the air entering the main body cabinet through the air suction inlet 2 from the casing 6 by the rotation of the centrifugal blower 7 generates a straight flow A which blows against the heat exchanger 4 at a right angle, a convective flow B which is generated at the upper, lower, left and right sides of the straight flow, and a parallel flow C which flows immediately before the heat exchanger 4 along the air suction surface of the heat exchanger 4.
FIG. 17 shows the flow immediately before the heat exchanger 4, and the parallel flow C which flows along the air suction surface of the heat exchanger 4 breaks away at the front ends of the fins 5 of the heat exchanger 4 and many breakaway flows D are further generated.
Since the prior-art ceiling built-in type air conditioner is structured as described above, noise like piping sound is generated due to the convective flow B, the parallel flow C and the breakaway flows D. We have confirmed that at the generated frequency of about 2 to 5 kHz, this noise becomes larger in proportion to the flow velocity of the passing air.
Further, the level of the noise changes depending on the distance between the heat exchanger and the air blowing outlet of the centrifugal blower casing, the size of the heat exchanger and the size of the air blowing outlet of the centrifugal blower casing. The noise of this type has become an increasing problem of abnormal noise under the environment of a higher demand for reducing noise of air conditioners and other noises in rooms.
Under these circumstances, as techniques for decreasing noise generated by the flow of blowing air from the fan to the heat exchanger, there have been disclosed a technique of providing a rectifying piece between the fan and the heat exchanger in Japanese Utility Model Application Laid-open (JP-U) No. 57-153916 and a technique of providing a rectifying plate in the air blowing outlet section of the fan in the Japanese Patent Application Laid-open (JP-A) No. 56-59148 respectively. However, according to the invention of the Japanese Utility Model Application Laidopen (JP-Th No. 57-153916, air is distributed properly into a heat exchanger coil by employing an oval or wing-shaped rectifying piece, and according to the invention of the Japanese Patent Application Laid-open (JP-A) No. 56-59148, a rectifying plate is provided at the air blowing outlet section of the fan. None of these inventions have the same structure and effects as the present invention.